Crop Rotation: Most of the disease, insect and weed problems you will have this season have already occurred and now in addition to maintaining your control of these you need to start thinking about next season. For many pests the severity of the problem next year will be the result of what you do this year. For insects and diseases the worst thing you can do is to give them a dependable food source year after year. The problem will likely get worse and worse. The most effective way to avoid this is by using crop rotation. Now is the time to decide where crop rotation will work to disrupt the dependable food source your insects and disease pathogens hope to find.

The effectiveness of crop rotation depends on the life history and biology of the particular pest. The three characteristics that play the biggest role are:

Dispersal Ability - How well and far can the pest move? If the pest can only move short distances then by rotating your crops to a new field you can leave them behind unable to reach food before they starve. On the other hand, if the pest typically moves long distances then moving your host crops will not make much difference. For example, the potato leaf hopper comes here all the way from the Gulf of Mexico region and so chances are that which field you decide to put your beans or potatoes in will not make much of a difference. In contrast, the Colorado potato beetle hibernates during the winter and essentially can only walk to potatoes when it wakes up in the spring. You do not have to move potatoes too far from last year’s field to significantly reduce the numbers that find the new planting.

Host Specificity - How many different kinds of plants does the pest or disease affect? If the pest is very specific in what it lives on it is easier to choose an alternative crop to plant where the pest is overwintering. On the other hand, if the pest feeds on many crops (or weeds) then it is difficult to avoid a food source for it and it will probably be waiting for you no matter where you move your crop or how long you wait to plant it again. For example, the tarnished plant bug, which is a major pest on lettuce (browning of the midrib), strawberries (catfacing), eggplant (feeds on tiny buds and they drop) and broccoli (brown beads in head), also feeds on about 300 weeds and so really does not depend on your crops to survive. In contrast, the species that causes Septoria leaf spot on tomato can only survive on plants in the tomato family (tomato, eggplant, potato, petunia, black nightshade, etc) so it is not that hard to plan a successful crop rotation to leave it without a host to feed on.

Persistance - How long can the pest survive without a host? This is a critical question because some diseases can persist in some sort of resting spore for very long periods of time waiting for a host to appear again. Most insects need food every season or they starve and many diseases can only survive a year or two without a host. For example, the pathogen that causes late blight of potato and tomato can only survive on living tissue and so in New England it really only makes it from season to season on potato tubers. Proper handling of culls is the key to managing this disease. In contrast, the pathogen that causes white mold of beans, carrots, tomato, lettuce, etc. can form resting bodies called sclerotia that are able to just sit in the soil for many years without any host. So, now is the time to look around the farm and see what you have for pests and learn which ones can be managed with crop rotation and then make plans. Crop rotation, in addition to a tool for pest management, is very important for managing nutrients in the soil and for controlling weeds.

Sanitation (Late Blight): Late blight is popping up in lots more locations now. It is not the epidemic proportion of gardens and farms that it was in 2009, but with the recent wet, cloudy and windy weather it has spread quite a bit. Late blight is one of those diseases for which sanitation, especially at the community and state level, is more important than crop rotation. The pathogen that causes the disease does not persist in the soil. In fact, here in New England it does not persist any where except in living host tissue. So, avoiding it next year is not dependent so much on which field you grow tomatoes or potatoes next year as much as it is on how you handle (and other folks in the region handle) the diseased tissue this year. Any of the plant parts that die will not carry the disease forward to next year, e.g., it is not able to persist on any part of a tomato plant unless you somehow keep that plant alive through the winter. And, it only persists on the potato tuber of the potato plant. The most common way it gets from one season to the next is by people planting diseased potatoes in the spring, or not scouting for and removing any potato plants that arose from cull potatoes laying around. Late blight is a great example of a disease that can be managed very well by simply having good sanitation.

Late Blight Update: Late blight is being found now in more sites in Maine. It is still quite spotty and nothing at all like the late blight storm of 2009. At this time, late blight has been found in the County (it is found there almost every year and is usually small and in spotty outbreaks that are well contained), in the mid-coast area confirmed on only one farm so far, and in Waldo County (including but not limited to towns such as Albion, Montville, Unity, China). Still, most of the pictures I am sent by folks suspecting late blight turn out to be early blight or Botrytis. It is time to be vigilant and scout your fields carefully, but don’t jump to any conclusions. If you are not positive it is late blight, do not take rash actions. But do not let late blight flourish under your watch and become a neighborhood problem. Get it positively identified and manage it well.

A Bit Of Biology: Late blight only overwinters in living tissue (the reason is a bit complicated and I don’t want to get into it here, but basically it is because there is no sexual reproduction taking place that would result in overwintering spores). That means here in the Northeast where it freezes in the winter there are very few places for the pathogen to live in the winter. The most common site of overwintering is the potato tuber. Using infected potato seed or not destroying infected volunteer potatoes from culls is the most common starting point of the disease most years. In 2009 it was different. Then it started with people bringing in infected tomato seedlings from southern locations where the pathogen does not freeze. In the spring the infected plants grow and so does the late blight fungus. It produces sporangia that are blown in the wind. Luckily the spores are whimpy and cannot tolerate sun light. But, if the conditions are cloudy and the leaves of plants are wet long enough, then spores that land germinate and start a new infection.

What If You See Symtoms? If symptoms of late blight are found in isolated areas in a planting, it may be possible to save the crop. Success depends on how early in disease development symptoms are found, how many infections are present that have not yet resulted in symptoms (symptoms do not appear until 7 days or so after spore germination), proximity to other farms or gardens that are carrying the infection, and what management steps are taken. If all of your plants are already showing symptoms, then it is probably too late. If you catch it early, immediately remove affected plant tissue and tissue near the infected parts. It is best to do this in the middle of a sunny day when the leaves are dry and any spores dislodged would be likely killed by the UV light and not germinate on dry leaves. Bag the diseased tissue so it does not release more spores, and get rid of it. Then apply an acceptable organic fungicide following the label directions.

Late Summer Diseases Rampant: This August has been wet. But even before we got the recent rains, August has been wet because it was very humid and the days are getting shorter. It is kind of sad for some people to see the days get shorter, and others that wake late in the morning don’t notice it, but the days are much shorter now. It gets dark by 8:00 and not light until after 5:00. Shorter days, the sun lower in the sky and especially the humidity being high for quite a few weeks have lead to heavy dew setting early in the evening and not evaporating until late morning. That means the leaves stay wet longer. What has developed in this seasonal situation, and weather, and late August crowded plants is disease. Many spores depend on a minimum number of hours for spore germination, and we got it in the past few weeks. All of a sudden some crops that looked great are on the edge of death, or over the edge.

Botrytis leaf blight. Photo by Eric Sideman.

Onions: Botrytis leaf blight has gone wild. Botrytis leaf blight is one of the most common fungal diseases of onion. Severity depends on the abundance of overwintering inoculum, and the number and duration of high humidity and leaf wetness periods, and moderate (50-70°F) temperatures.

When conditions are favorable it can take down an entire field. The disease often results in smaller bulbs and lower yield. Symptoms are whitish lesions on the leaves, usually at first having a greenish halo, then developing into a sunken, yellowish spot with a characteristic slit oriented lengthwise to the stem. Symptoms tend to appear first on older leaves.

As the disease progresses the lesions coalesce and leaves yellow and die back. Massive numbers of conidia (spores) are released from infected leaves and are wind blown to new plants.

Botrytis overwinters as sclerotia, which were formed on infected tissue and appear as tiny black specks. Dead leaves and culls left in the field or in piles over winter are the source of new infections. The sclerotia germinate in the spring and release spores, which infect young onion plants.

Minimizing the leaf and cull bulb tissue left on the soil surface after harvest is key to management. Culls should be destroyed, not piled. Volunteer onion plants in the spring should be rougued. Crop residue should be removed from the field at harvest or plowed deeply. Crop rotation is effective if new field is well apart from the old field.

Minimizing periods of leaf wetness is key. Wide row spacing and within row spacing allows more air movement. Double or triple rows on wet years will lead to a problem. Overhead irrigation should be very early morning on sunny days to allow for quick drying and not extend the period of wetness from dew.

Serenade (Bacillus subtilis) has been shown to be effective in at least one study.

Tomatoes: Early blight and Septoria leaf spot are much more common than late blight. In fact, most field tomatoes are showing these now to a greater or lesser extent. Some field tomatoes are mostly dead now due to these two diseases.

Both of these diseases begin on the lower leaves of the plant. Early blight begins with large spots that have concentric rings sort of like an oyster shell. The leaves turn yellow around the spot and then the whole leaf may turn yellow These spots usually coalesce and whole leaves turn brown. Early blight will take down potatoes as well as tomatoes. This is when photos are taken and sent to me by folks who think they have late blight.

Septoria leaf spots are small and develop a gray center. Many small spots occur on the leaf and the leaf usually turns yellow. These spots occur on the stems too, and they may coalesce and from a brown to black large patch on the leaf or stem. This is when photos are taken and sent to me by folks who think they have late blight.

Both of these disease overwinter on tomato debris that is left in the garden. Unlike late blight, these pathogens survive on dead tissue. In the spring, spores are splashed up from the soil and that is why the diseases usually start on the lower part of the plant. Later in the season spores of these diseases are blowing all over the place and it is hard to avoid them. Most commercial tomato growers have gone to raising tomatoes in high tunnels where they can avoid these blowing spores and keep the tomato leaves dry to prevent germination of any that get in. Anything you can do to minimize tomato debris, splashing spores, and leaf wetness will help.

Winter Squash: If you did not spot the powdery mildew (Pest Report-August 4) that arrived in early August and treat for it your pumpkins and most winter squash is going down to it now. Cucumbers and melons are resistant to it, but are going down now to a myriad of other problems. And, to add to the collapse of cucurbits, the squash bugs (Pest Report-July 8) you may have ignored are now taking down the plants. Whole leaves turn brown due to toxins they inject when they feed.

Gray Mold: There are a bunch of species of Botrytis but the one that causes gray mold has taken off in the humid weather and crowded garden conditions. The most common places you see this include soft ripe fruit after picking (ex. raspberries), tomatoes in humid greenhouses, tomatoes crowded in gardens, lettuce planted too close, and many flowers. Sanitation helps because leaving the fuzzy, gray mass of spores around is asking for problems. But, by far, the most important practice is to keep the air moving and drying the flowers, leaves and fruit. Of course, if the air is 100% humid it will help little.

Late blight seems to have popped up at more sites this weekend, especially central coast. I have received pictures from three different farms that are suspicious. There has not been lab confirmation yet, but it sure looks like late blight and it is time to really get alert.

Rainy, humid, cloudy conditions have provided favorable conditions for the pathogen to successfully be dispersed long distances and for infection to take place. Clouds protect spores being dispersed in wind from the killing effect of UV radiation.

All growers, including gardeners, should thoroughly inspect their potato and tomato plantings because this can be a very destructive disease when not managed, quickly killing foliage and rotting tomato fruit and potato tubers, AND be a source of spores spreading the disease to other growers.

Classic symptoms are large (at least nickel sized) olive green to brown spots on leaves with slightly fuzzy white fungal growth on the underside when conditions have been humid (early morning or after rain, or if it is dry you can induce it for identification by putting an infected leaf in a plastic bag over night). Sometimes the lesion border is yellow, but not usually. Often it has a water-soaked appearance. Leaf lesions begin as tiny, irregularly-shaped brown spots. Brown to blackish lesions also develop on upper stems. Firm, brown spots develop on tomato fruit. There are great photographs at:

If you believe you have the disease, get a sample to your local Extension office, or send me a picture. Still, most of the suspects are proving to be early blight or Botrytis, so don’t jump to conclusions.

If you find late blight in a localized spot in a field or garden, promptly destroy all symptomatic plants plus a border of surrounding plants to eliminate this source of inoculum. Physically pull, bag and get rid of affected plants. (This is done to prevent the spores from spreading to other farms.) Do not just drop in field as they will still be a source of spores. If disking is used to destroy a whole field, the crop should first be sprayed with fungicide because of the potential to move spores on equipment especially while driving out of the field, and the equipment should be pressure washed afterwards.

If you feel you have found late blight in only a localized spot, and most of your field is still clean of the disease, then you may want to spray a copper based fungicide. Copper products have proven to give good control, if sprayed before infection has occurred. DO NOT USE AT RATES OR FREQUENCY BEYOND LABEL INSTRUCTIONS.

[The legal Champ WP rate in the greenhouse is the same rate as in the field, that being 1 to 1.5 pounds (up to 4 pounds in severe cases) per acre for potatoes and 2 to 4 pounds per acre for tomatoes.

Greenhouse tomato coverage is about 1 ounce per square foot (the 1 ounce per square foot rate is equivalent to 340 gallons per acre in a field rate). Two level tablespoons of Champ WG per 1000 square feet of greenhouse is equivalent to 1 pound per acre. One level tablespoon of Champ WG per gallon of water is equivalent to 1 pound per 100 gallons.]

REMEMBER, only certain formulations of copper fungicides are allowed in organic production. Be sure to check with your certifier if you are not sure. Common formulations include Champ WG, Cueva Fungicide Concentrate, and COC WP.

Some of this information on management was provided by Dr. Steve Johnson, University of Maine Cooperative Extension, and Drs. Meg McGrath and Tom Zitter, Cornell University.

Late Blight Update: Late blight has been found this week in a garden in Vermont. It still remains only in a small number of isolated spots around the Northeast (one in the County in Maine, a garden in Vermont, a few farms in New York on Long Island, etc.). It is not time for tears or fear yet, BUT it is time for vigilance. Be sure to scout your potatoes and tomatoes frequently. If you find a problem and suspect late blight, please send me a picture (in focus please). If I suspect late blight, but it is not a clear case, then I will suggest you send a sample to the Pest Management Office for positive identification. At this time, none of the many pictures I have received have been late blight. At this time, early blight and septoria leaf spot are common, and in some damp situations Botrytis is popping up. Here is a great site with good pictures:

Hornworms (Manduca quinquemaculata and Manduca sexta): Hornworms are probably the most destructive insect attacking tomatoes and they are showing up now. They are giant caterpillars that can do a vast amount of eating in a very short time. Sometimes it seems that overnight healthy looking tomato or pepper plants are striped of their leaves leaving bare stems. The hornworms will also attack the fruit eating gouges out so large that they look more like bites of a furry animal than an insect. Look now for the damage and the frass, which is black pellets laying all around plants hosting hornworms. The frass may be your first sign there is a problem.

The adults are large, fast flying hawk moths, which in flight may look like a hummingbird. At dusk they hover over flowers sucking nectar. Eggs are laid on tomato leaves and hatch in 5 days.

Hand picking is a bit frightening but does work and chickens enjoy fighting with the challenging pest. The problem with hand picking is that they blend in very well and it is easy to overlook one or two caterpillars, which can do significant damage in a day or two.

Bt works very well on this caterpillar, especially when they are small.

Tomato hornworm with Braconid wasp cocoons. Photo by Eric Sideman.

What Are Those White Things On The Hornworms? Tomato hornworm larvae are parasitized by a number of insects. One of the most common is a small braconid wasp, Cotesia congregatus. Larvae that hatch from wasp eggs laid on the hornworm feed on the inside of the hornworm until the wasp is ready to pupate. The cocoons appear as many small white projections protruding from the hornworm‚s body. Parasitized hornworms should be left in the field to conserve the beneficial parasitoids. The wasps will kill the hornworms when they emerge from the cocoons and will seek out other hornworms to parasitize. (reprinted from 2005 Vermont Veg and Berry News by Vern Grubinger)

Powdery Mildew (Podosphaera xanthii): Powdery mildew is a common disease of pumpkins and winter squash. All cucurbits are susceptible, but many common cucumber and melon varieties are resistant. The disease can cause infected leaves to die prematurely, reducing yields and lowering fruit quality, especially taste. Winter squash from diseased plants won’t store as long as fruits from healthy plants, nor will it be as sweet because late season sugar production is important to squash quality and with no leaves there is no sugar production.

First spots of powdery mildew. Photo by Eric Sideman.

The fungus that causes the disease does not overwinter in Maine. Spores blow up every year from southern overwintering sites. If they arrive late in the season, you may not need any control; but if they arrive in early to midsummer, exercise some control or you may have no leaves by mid-August.

Powdery mildew reports are now coming in to me. This may warrant attention. Go out and scout.

Check upper and lower surfaces of leaves of older plants every few days starting now. The first symptoms usually are white, powdery fungal patches on the undersides of older leaves. Yellow spots may form opposite these, on the upper leaf surfaces.

No products with systemic activity (products that move through the plant) are approved for organic production, and applying fungicide to the lower leaf surface is difficult. In experiments, foliar applications of sulfur have been more effective than most other organic products for powdery mildew, apparently because sulfur deposited on the upper leaf surface can volatilize and be redistributed to the lower surface. Sulfur can be phytotoxic on melons, especially if applied when temperatures are hot.

ATTRA (National Sustainable Agriculture Information Service, www.attra.ncat.org) reports that a single spray application (to runoff) of 0.5 percent (wt./vol. of water) baking soda, plus 0.5 percent (vol./vol. of water) SunSpray UFP® horticultural oil almost completely inhibited powdery mildew on heavily infected pumpkin foliage; while baking soda without the oil was ineffective, and a 2 percent (wt./vol. of water) solution of baking soda damaged the leaves. But, remember if you are a commercial grower then you should be using EPA registered pesticides and not homemade concoctions.

Mexican Bean Beetle Larva. Photo by Eric Sideman.

Mexican Bean Beetle (Epilachna varivestis): The Mexican bean beetle is one of the few members of the lady beetle family that has evolved to feed on plants rather than be a predator of other insects. It is a somewhat spotty pest in the Northeast with many farms never seeing one and others having crops devoured year after year. This year I have received a few reports already. This beetle feeds on snap and dry beans primarily, and may be seen feeding on soybeans or cowpeas sometimes. The larvae skeletonize leaves turning them into lace. The adults feed on leaves and pods too. The adult looks like a lady beetle with 8 black spots arranged in rows across the body that may range in color from rust to yellow. The larvae are very spiny, slow moving critters that are bright yellow.

The Mexican bean beetle spends the winter as an adult hiding in trashy and weedy areas along the edges of fields. They move into fields in the late spring to early summer and feed for about a week or two before the females lay groups of orange eggs on the underside of leaves. These hatch in a week or two and the larvae will feed for about three weeks. The reports I am getting now are larva, which, I guess, are weird enough to prompt a call to me. The larvae pupate and a new generation of adults emerge in about 10 days. The worst damage from this pest occurs in late July and August. Near New York City there are two generations per season while in the north there is only one.

Moderate control can be achieved with Entrust as well as mixtures of pyrethrin (PyGanic EC5.0) and Neemix.

For next year, discourage hibernating beetles by cleaning up all plant debris after harvest. Maintain wide, clean headlands and brushless wood edges. Plow under crop debris shortly after harvest.

Biological control is proving very effective. Pediobius foveolatus is a wasp that lays its eggs in the larva. The wasp larvae feed inside the MBB larva and eventually kill it. About 25 new wasps emerge from each killed MBB larva and so control actually gets better as the season progresses. Plan on making the release of the wasp as soon as the pest is present, not before nor after it has built up to damaging numbers. It is recommended to make two releases two weeks in a row. It is too late for this year, but if you have it, be prepared for next year to see it again.

Garlic: Growers have either harvested their garlic, or will be harvesting soon. There are two diseases that are not common here in New England and we want to keep it that way. Now is the time to look and see if you have either of them. As you harvest, please inspect your bulbs carefully. Both of these diseases are devastating and long lasting in the field, preventing future garlic production. And, both are spread with the garlic seed pieces so it is of the utmost importance that anyone with this problem not sell seed.

White rote of garlic. Photo by Eric Sideman.

White Rot of Garlic (Sclerotium cepivorum)- White rot is a very serious problem because it may spread fast, and once in a field it can persist for many years. Luckily it is a spotty disease and at this time is only present in a small number of fields around the northeast. Those farms can no longer grow Allium in infested fields.

White rot is one of the most destructive fungal diseases affecting the onion family. It is only a problem on crops in the onion family. [It is not the same pathogen as white mold, which attacks many other crops such as beans, carrots, lettuce, tomatos, peppers and more]. Symptoms of white rot on the leaves include premature yellowing and dying of the older leaves and then death of the plant. That is not much different than many other garlic problems so is not a very useful diagnostic symptom, but the white, fluffy fungal growth (mycelia) on the root end of the bulb is the give away. Eventually this fungal growth moves around the bulb and inward between the storage leaves of onion and cloves of garlic. Small, black sclerotia (tiny hard, black bodies of dormant mycelia) form in the decaying tissue and throughout the white fluffy mycelia. Secondary infections by other fungi may occur.

The pathogen is not known to produce spores. This fungus reproduces only by the sclerotia, and it also spreads by direct contact, i.e., when the mycelium growing on one plant reaches the roots of the neighbor plant in the row. The sclerotia can lie dormant in the soil for many years until roots of a host plant grows nearby and the sclerotia are stimulated to germinate (see below). Dragging the pathogen around on boots, tillage or other equipment, or moving with soil in heavy rains are other ways the disease spreads. Also, animals feeding on diseased bulbs can defecate viable sclerotia.

The best control is good sanitation. Use clean seed cloves for garlic and clean onion sets and transplants. If only a small number of plants are infected, which is usually the case the first year it is found on a farm, pull the infected plants and destroy before sclerotia are formed.

An interesting idea for speeding up the eradication of white rot sclerotia from the soil is to stimulate them to germinate but not have a crop of Alliums for them. Sclerotia will sit waiting in the soil for 20 or more years until a signal is received that onions or garlic are growing nearby. The growing Allium releases a chemical that the sclerotia can sense. Over the past decade researchers have been studying methods that stimulate the sclerotia to germinate but, of course, with no Allium crop growing for the pathogen to complete its life cycle. This "biostimulation" reduces the number of sclerotia in the soil. There is not a specific recommendation yet, but a few things that may reduce sclerotia in the soil include:

growing scallions which stimulate the sclerotia to germinate, but the scallions are harvested before the disease completes its life cycle

making compost out of onion or garlic waste and spreading that in the spring or fall repeated for a bunch of years before trying to grow an Allium again

making a sprayable concoction from ground up onion or garlic waste, or using garlic powder as a soil amendment for a few years before trying to go back to an Allium

If the disease is known to be present, or if onions from other farms are being stored and packed, equipment, storage bins, etc. should be thoroughly pressure-washed and then disinfested for ten minutes with a 0.5% solution of sodium or calcium hypochlorite, (for example, 1:10 dilution of a household bleach). Then rinse with potable water.

Seed producers should execute extra diligence and may want to regularly disinfect any surface in contact with garlic.
Since chlorine materials will be inactivated by organic matter stuck on boots, quaternary ammonium compounds may be used as boot dips inside storage areas and packing sheds, and before and after leaving fields. Quaternary should not be used on any apparatus that is in direct contact with the garlic or onions or any other crop. Disposal of the dip solution must be in a manner that does not contaminate the soil, water or crop. Note: not all quaternary ammonium products are labeled for boot washes so read the label.

Garlic Bulb Nematode (Ditylenchus dipsaci)- The garlic bulb nematode, also called the garlic bloat nematode, is a new garlic pest that first appeared during the wet year of 2009, with confirmed cases in New York and Vermont. It is now in New Hampshire and Maine too, brought in with garlic seed purchases. The microscopic worms feed by piercing root and leaf cells with their stylet. Leaves of severely infected plants turn yellow and dry prematurely. Plants may be stunted. The roots may be missing and the basal plate may appear to have a dry rot similar to Fusarium basal plate rot.

The pest is favored by wet, cool conditions. Although the pest is not active in hot dry weather, such weather may exacerbate symptoms. The nematode survives freezing and hot weather in soil and plant debris.

The best way to avoid garlic bulb nematode is to use your own garlic for seed, if it is not yet infested. Monitor for symptoms of infestation during the growing season and submit suspect plants to a diagnostic lab for confirmation. Both UNH and UMO can ID this pest for you. Contact the lab to get instructions how to take and where to send the sample.

If it is determined that you do have the problem, do not use your own garlic for seed, or sell the seed. Even bulbs that show no symptoms may have low leves of infestation. Obviously, do not sell any garlic for seed from a potentially infested lot. Do not replant garlic in an infested field for at least four years. Other hosts include all Alliums, celery, parsley, and salsify. Mustards, Sorghum-sudan grass, and other bio-fumigant cover crops have been shown to reduce nematode populations. These nematodes can survive in dry debris so carefully clean equipment and storage areas.

There are no materials approved for organic production.

Purple blotch on garlic leaves. Photo by Eric Sideman.

Purple Blotch (Alternaria porri) - Purple blotch is a very common and sometime destructive disease that affects onions, garlic, shallots and leeks. It is not as devastating as the other two, but much more common. Lesions begin as whitish sunken areas that elongate and develop purplish centers. Under favorable conditions (warm with wet leaves) the lesions become large and oval with concentric rings of spores. The lesions may merge and take down whole leaves, which may become covered with brownish spores. The older leaves are more susceptible than the younger leaves. This pathogen may also result in a watery rot at the neck of onions or garlic and lead to poor storage life.

Onion residue is the source of the disease in the spring. The fungal mycelium and conidia (spores) persist as long as the onion debris remains in the field or in cull piles. New conidia are produced on infected tissue in the spring and wind blown or carried in water to the new crop. The leaves must be wet for the spores to germinate, but germination is very quick, less than an hour. Symptoms may appear in less than a week after germination and new spores are quickly produced.

Sanitation is very important to limiting spread. Infected crop debris should be destroyed or buried after harvest. Cull piles should be eliminated. Grow onions in rotation with non-host crops.

Serenade has been shown to be effective against purple blotch. Copper has demonstrated mixed results in trials, fair at best.

Late blight has been found in Carbou, Maine. We have no details yet, but the disease is close enough that we should be very vigilant. Scout your potato and tomato fields frequently. Good pictures can be found at the following website to help you identify the problem, or you can look back at previous Pest Reports.

If you think you may have late blight on your plants but are not certain, please send a good quality, digital photograph to me at esideman@mofga.org and I will let you know if I can identify it. If it's a "maybe", then I will instruct you to send a sample up to the Pest Management Office for positive ID.

I do not think the risk level is high. We do not have the weather in most of Maine that would favor quick spread of the disease, nor do we have wide spread inoculum. But, we all have to be good neighbors and monitor our plantings so we do not develop wide spread inoculum.MOFGA's Pest Report - July 8, 2011
Compiled by Eric Sideman, PhD - MOFGA's Organic Crop Specialist

Late Blight: At this time there are no active reports of late blight closer than Long Island, New York. I will send out an “UPDATE” if things change, and an “ALERT” if it, or something else very serious, gets to be an immediate threat. If you are not already on my Pest Report Email List, send me an email and I'll add you to the list.

Squash Vine Borer: (Adapted from an article in the U Mass Vegetable Notes). Squash vine borers are showing up in traps in NH at their highest level in 5 years, and squash bugs (see below) have been seen colonizing cucurbit crops. Many vine crops are in bloom, and care should be taken during bloom to avoid insecticides which are toxic to pollinators, e.g., pyrethrum.

Squash vine borer moths are day-flying moths with a 1.0 to 1.5 inch wingspan and bright orange markings. In flight, they look like wasps. There is one generation each year and adults emerge in late June/early July. They lay eggs at the base of squash plants, and upon hatching, larvae bore into stems (where they are protected from insecticides). Thick-stemmed squashes are preferred. Unless you use traps or scout fields for evidence of eggs or larvae, the first sign of squash vine borer infestation is often wilting vines in July and August. By that time, it is too late to do anything.

Growers should scout their pumpkin and squash fields weekly for squash vine borer from late June through early August. Examine the base of vines for evidence of larval feeding (sawdust-like frass near entrance holes) and then split open the stem to confirm the presence of larvae, which suggests more eggs are being laid. Two insecticide sprays, ideally applied to the base of the plants and timed five to seven days apart, will control newly hatching larvae before they are able to bore into the stem. Treat base of stems thoroughly to target hatching larvae. Spinosad (Entrust) provides excellent control of hatching SVB larvae if you catch them before they bore into the stem.

Alternatively, you can monitor with a Scentry Heliothis pheromone trap from early June through early August. Make 2 to 4 weekly applications if more than 5 moths per week are captured. Timing is very important. - Source material from New England Vegetable Management Guide; Handbook of Vegetable Pests, A Capinera; ATTRA.
Adapted by Andy Cavanagh & R Hazzard, UMass Extension.

Squash Bug: (Adapted from an article in the U Mass Vegetable Notes). Squash bugs (Anasis tristis) are serious pests of pumpkins and squash throughout North America. Damage and survival are low on watermelon, very low on cucumber and muskmelon, and highest on squash and pumpkin. Both adults and nymphs feed by inserting their beak and sucking juices from plant tissue. Toxic saliva injected during feeding causes foliage to wilt, then turn black and die; the severity of this damage is directly related to density of squash bugs on each plant. Later in the season, squash bugs may feed on the fruit, causing them to collapse or become unmarketable.

Adults are 0.5 to 0.75 of an inch long, flattened and grayish-brown. They hibernate in trash in and around the garden for the winter and emerge in the early summer to feed a bit and lay eggs. Eggs are laid in clusters usually on the underside of leaves and are orange when first laid, but turn bronze-colored before they hatch. The wingless nymphs are similar in appearance to adults, and are whitish when small, with a brown head, and grayish white when larger with black legs. There is one generation per year in the Northeast.

Squash bug numbers are reduced by clean cultivation in the fall, and crop rotation. Infestation is delayed by row covers. If possible, rotate cucurbit crops between fields as far apart as possible. Keep headlands mowed and free of trash to reduce overwintering sites.

Squash bugs are unusually difficult to control with insecticides. Scout undersides of leaves for squash bug adults and eggs. Crush the eggs, but you may not want to crush the bugs as they stink when you do. Treat if the copper-colored egg masses exceed one per plant. Time squash bug sprays to kill young nymphs just after hatch, because this stage is the easiest to control. Treat late in the day when the flowers are closed to reduce risk to bees. Neem products have proved effective.

For adult bug control, insecticides applied to the base of the plant are most effective, possibly because bugs tend to cluster. But, squash bugs are virtually impossible to control later in the season when nymphs are large and the canopy is dense. - Source material from New England Vegetable Management Guide; Handbook of Vegetable Pests, A Capinera; ATTRA. Adapted by Andy Cavanagh & R Hazzard, UMass Extension.

Squash bug adult and eggs.

Squash bug young nymphs and eggs.

Squash bug older nymphs.

Photos by Eric Sideman.

Caterpillars In Brassica Crops: There are three common caterpillars that feed on our broccoli family crops. Keep an eye out for them. The imported cabbageworm butterflies are flying now.

Quick ID Cues

Diamondback moth caterpillar: Green, very wiggly when poked, pointed on both ends, not fuzzy, only grows to about 1/2 inch. You may find white silken cocoons. They eat wholes in the leaves. There are many generations in a single season, even though they do not overwinter here.

Imported cabbageworm: gray-green, slightly fuzzy, and sluggish. Grows to >1 inch and favors the center of the head as it gets larger. Leaves wet green frass (droppings). Eggs single, light green or yellow. They eat large chunks out of leaves. The adults are those white butterflies you commonly see flying around your broccoli.

Cabbage looper: light green, smooth, loops up like an inch worm as it moves. Eats big holes in leaves. Scout undersides of leaves to look for fresh damage, and get control of the caterpillars when they are small and damage is slight. Check heading crops as soon as heads start to form. Greens should be scouted at all growth stages.

For organic growers both Bt and Spinosad are very effective (Bt products are a lot cheaper), but remember to only spray after scouting and assessing damage. The pest has to be there to be killed, i.e., neither material has long efficacy after spraying. Destroy crop after harvest so it does not act as a harbor for the pests all season.

Diamondback larvae

Imported cabbage worm.

Photos by Eric Sideman.

Rose Chafer: The rose chafer is in the same family of beetles as the Japanese beetle and has a similar life history.

The adult is out now and voraciously feeding on many different crops such as rose, raspberries, apples, grapes and some vegetables too. They skeletonize the leaves and are feeding on blossoms and young fruit too.

The adult is a half inch long, gray-tan beetle with a reddish-brown head. The adults are mating now and will lay white, shiny eggs in the soil soon. The larvae are white grubs that live in sod feeding on roots, especially on sandy ground. The life span of the adult is only about three weeks so you may just want to wait them out. But if your population is large you may loose your crop while you wait.

Crop rotation will not help because they are good fliers. You may be able to control grubs with beneficial nematodes, but that is likely to help little with controlling adults because your neighbor's sod ground will be a source even if yours is not. Hand picking or knocking the critter off the leaf into a jar of water works well for small plantings. Pyganic and Surround seem to do little to deter adults. Rotenone may work, but there are no formulations permitted in organic production and its EPA registration as an insecticide has been dropped. I have heard from a grower that neem oil works well, especially a neem and diatomaceous earth combo. Has anyone else tried that with success? Are there any other suggestions?

Leafhoppers: (repeated from June 23 issue because this is important). Potato Leafhoppers (PLH) have made it to Maine. I have just received a report of them in Wells on beans and they have been in southern New Hampshire for a while. They are likely to be moving north so be on the lookout. They also feed on potatoes, strawberries and alfalfa.. PLH does not over winter anywhere near here. They over winter way down south and leapfrog up here in mass migrations. The first to arrive are females, and they are usually carrying fertilized eggs when they get here. Then there are a few generations over the growing season before the cold north winter kills them.

The damage from leafhopper is catastrophic. The bug sucks the juice out of the plant and injects a toxin that clogs the food conducting tissue. The symptoms look like a disease after a while rather than insect damage. The leaves first get pale, then yellow and then brown from the edges. Then the plant dies. The symptoms are called hopper burn.

The adult PLH is very light green and wedge shaped and tiny (an eighth of an inch long). The best way to find them is to brush the plant and watch one of the white-looking bugs land. The nymphs are similar to the adult, but have no wings and are smaller and live on the underside of the leaves. If you disturb a nymph you will see it run and it can run sideways as fast as forward. This is a clue that you have PLH and not some other less harmful leafhopper.
The adults are flighty. When you brush your crop you will see them fly up. If there is a cloud, you are in trouble. If there is only one or two in a row of plants your crop will probably not be hurt badly. That is why researchers have developed a threshold before treatment is recommended. For example, on beans a population equal or exceeding an average of one nymph per leaf, or fifty adults per ten sweeps with a net means it is time to spray.

Crop rotation does nothing for you since they are coming from far away. Covering you crops with a row cover would work, but these crops are not the type that are usually covered. Effective insecticides are limited. The only material that I have seen work that is allowed in organic production is pyrethrum, so Pyganic is the recommendation that I make. However, it does not work that well. Spray late in the day or evening, get good coverage including the undersides of the leaves, and don't wait until it is too late.

Growers with diverse crops and small plantings often need to be able to apply pesticide to beds or plots of several hundred square feet rather than acres, and the pesticide labels often only give rates on per acre basis. It is important to use the correct amount of insecticide in your backpack sprayer when spraying a small area. Calibration and mixing require some basic math, as do a lot of aspects of farming! The methods for backpack sprayers and tractor sprayers are essentially the same. Figure out the area to be sprayed and how much pesticide is needed for that area. Measure the amount of water you need to cover a known area, using the same equipment and walking or driving speed that you will use when spraying. Then ‘do the math’ so that the insecticide and the water rates both match your target area. Why does it matter? Why do you need to be careful about these rates? 1. Effective control of the pest depends on correct rates. 2. You are legally responsible for following the label instructions. This is especially important when you are selling the crop to the public. 3. The safety of the applicator, workers and the public depends upon correct rates and using pesticides according to instructions on the label.

Read the label. Find and follow the following instructions: --Personal protective equipment (PPE) – what you must wear when mixing and spraying. --Agricultural Use Requirements – this tells what protective equipment you should wear. --Crops and pests listed. The pesticide MUST be labeled for the target crop. --Restricted Entry Interval (REI) – during this time, no one should work in the sprayed area unless they are wearing protective equipment. --Days to Harvest (DH) – how long you must wait after a spray before harvesting (note: days to harvest may be less than REI; it is not a misprint) --Rate per acre or concentration per gallon (for backpack sprayer) --Mixing instructions.

The label often uses inconvenient measures. Conversions are key to your calculations. Here are some conversion ratios: 16 dry oz (by wt) = 1 lb One ounce (dry weight) equals 28.45 grams. 32 fl oz = 1 qt. 128 fl oz = 1 gal Liquid measure in (fluid) ounces is already a volume so it is easier to measure. One fluid ounce equals 6 teaspoons (tsp) or 29.6 milliliters (ml). An inexpensive measuring device for ml can be found in the children’s medicine section of drug stores. 43560 sq ft = 1 acre. Entrust, for example- Based on repeated samples, we have found that there is 1.7 gm per teaspoon (shaved level and tamped slightly). So for Entrust the recommendation is 1.3 grams (3/4 teaspoon) in 3 gallons of water for 1,000 sq. ft.MOFGA's Pest Report - June 30, 2011
Compiled by Eric Sideman, PhD - MOFGA's Organic Crop Specialist

Late Blight Update And Other Tomato And Potato Spots: At this time late blight is not being reported in New England. BUT, there was a recent report in New York, on Long Island. At this time, it is restricted to a few farms. Remember, things can change quickly. It is time to be vigilant and be out scouting, especially if the weather becomes wet again.

Also, you should learn to recognize some other tomato problems. Be ready and able to distinguish the common blights and spots. Don’t jump to the conclusion that you have late blight. Here is a website with great pictures:

The three most common problems with tomatoes grown in the field in Maine are Early Blight (potatoes too), Bacterial (Spot and Speck) and Septoria Leaf Spot. It is early, but it is time to start looking if you want to get some control on them. Other issues that may sometime trick growers into thinking they have late blight are heat stress and Botrytis. See that website above for pictures of all of these.

Bacterial Speck starts as dark brown to black spots on leaves that later develop yellow halos around the area effected. On the fruit black specks develop that rarely get larger than 1 mm . Bacterial Spot starts as brownish, circular spots that may become as large as 3mm and irregular. The diseases may be seed borne and may be carried over in weeds. High humidity and low temperatures favor bacterial speck.

Early blight of tomato is caused by fungi and starts on the lower leaves as small circular spots that have a target appearance of concentric rings. Leaves develop yellow blighted areas as the spots enlarge. Later the tomato fruit may rot on the stem end. The disease is carried over on tomato residue in the soil and can be seed borne.

Septoria Leaf Spot is a fungal disease that starts as spots on the lower leaves that have a dark brown margin and a tan center, and no target appearance. Rapid defoliation can occur.

Crop rotation is the first line of defense from all of these problems. Sanitation is important, especially for late blight that only survives the winter on living tissue such as the potato tuber. Do not grow tomatoes or potatoes near cull piles of last year's crops. Trellising, staking, cages, etc help but remember to disinfect if they were used last year (a 10:1 dilution of household bleach is effective). Prune off diseased lower leaves, but it is especially important to disinfect tools if the problem is one of the bacterial diseases. Avoid working in the crops when they are wet. Scouting is going to be important this year. With wet weather, start early and if you decide to use a material, copper is probably the one most effective for us organic growers. Remember, you MUST use a formulation that is approved for organic production. The ones that I know are approved are Champ WG, NuCop 50 WP. Others may be but check with your certifier BEFORE using. You must use copper in a way that does not lead to contamination of the soil or crop. Follow the label instructions, and maintain a good crop rotation to avoid use of copper in the same field too frequently. Regularly do soil testing to monitor your copper levels.

Update: The cool weather has slowed the progress of things, including pests. There have been only a few new developments this week. Colorado potato beetle adults are active and laying eggs (see below). I am getting reports about dying cabbage and broccoli from the cabbage maggot feeding (Pest Report of April 11), but that damage is from the pest activity back in April and May. That risk is much less now as they do not do well in warm soil. There is still cutworm activity (Pest Report of May 9). I did get a report that the new product called Seduce recommended in that Pest Report has worked very well. Flea beetles are much less of a problem now. And, the cucumber beetle is spotty with some folks not seeing any and others being hit hard. Please send me reports of pests and diseases that you are seeing that have not yet been covered. Send to esideman@mofga.org.

Colorado Potato Beetle (Leptinotarsa decemlineata): Colorado potato beetles (CPB) adults are just starting to show up in potato and eggplant crops. The bright yellow eggs are laid in clumps with about 30-35 eggs each, generally on the undersides of leaves. As with most other insects and plants, there is a direct relationship between higher temperatures (in the range between about 55 and 90 degrees F) and faster rate of development. That includes egg-laying, egg hatch, larval growth, and feeding rates. A period of cold, rainy weather slows everything down, but we can expect a surge of adults and shiny yellow eggs to appear with the next hot spell.

Colorado Potato Beetle. Photo by Eric Sideman.

Scouting and Thresholds: Walk your fields NOW and look for CPB adults and eggs. A treatment should be considered for adults when you find 25 beetles per 50 plants and defoliation has reached the 10% level. The spray threshold for small larvae is 4 per plant; for large larvae, 1.5 per plant (or per stalk in midseason), based on a count of 50 plants or stalks.

Colorado Potato Beetle eggs. Photo by Eric Sideman.

Controls are needed on eggplants when there are 2 small or 1 large larvae per plant (if plants are less than six inches) and 4 small larvae or 2 large per plant (if plants are more than six inches).

Potatoes can tolerate 20% defoliation without reduction in yield (or even more late in the season and cultivar). Damage to eggplant seedlings from adult feeding is often severe enough to warrant control of the adults. In potato, adult damage in rotated fields may not be significant, so you may be able to wait until after egg hatch to kill both adults and larvae. Look on the undersides of leaves for the orange-yellow egg masses. The fresher the eggs, the brighter orange the eggs will appear. Eggs hatch in 7-10 days, depending on temperature. If you want to know when the earliest eggs are hatching, you can flag a few of the earliest egg masses you find with bright tape or flags, and then keep an eye on the hatch.

Colorado Potato Beetle larvae and damage. Photo by Eric Sideman.

Hatched larvae go through four stages before they become adults. In the first stage, the larvae are about the same size as the eggs and in the second stage they are about an eighth of an inch long. As the larvae get bigger, they do more feeding. The fourth, or largest, stage does 85% of the feeding damage. It’s a good idea to prevent beetles from ever reaching the fourth instar!

After larvae complete their growth, they drop to the ground and burrow into the ground to pupate. About ten days later the next generation of adults emerges – ready to feed. If they emerge before August 1, they will lay more eggs. After August 1, they feed and head to overwintering sites. Good control in June prevents problems with CPB in August.

Cultural Controls

Crop Rotation. The single most important tactic for CPB management is to rotate potatoes or eggplant to a field that is at least 200 yards from the previous year’s fields. Since the adult that comes out of winter cannot fly, barriers such as roads, rivers, woodlands, and fields with other crops are helpful. Rotated fields tend to be colonized 1-4 weeks later in the season than non rotated fields. Also, the total population of adult beetles is lower, producing fewer larvae to control.

Perimeter treatments or perimeter trap cropping can be applied to potato. One approach is to plant a barrier crop between overwintering sites and this year’s crop and get it in earlier than the main crop; then control early-arriving beetles.

Early planting. Green sprouting, also know as chitting, prepares whole seed potatoes to emerge rapidly, gaining about 7-10 days to harvest. This early start makes it easier for the crop to put on growth and size before CPB adults and larvae arrive. It can be combined with raised beds and plasticulture. While it won’t avoid damage altogether, it may reduce the need for insecticides. Refer to the New England Vegetable Management Guide (online at www.nevegetable.org) for more details.

Late planting. Another strategy for beating the beetle is to plant late. CPB adults that do not find food leave the field in search of greener pastures. Planting after mid- June, using a short season variety, often avoids CPB damage and eliminates the need for controls.

Straw mulch. It has been well documented that when potato or eggplants are mulched with straw, fewer Colorado potato beetle adults will settle on the plants and fewer eggs will be laid. This can be accomplished on larger plantings by strip planting in a rye mulch, followed by mowing and pushing the rye straw over the plants after they emerge. For smaller plots, straw may be carried in.

Organic materials for control. Spinosad (Entrust) and azadiractin (AZA-Direct) are two options. Recent studies have shown very good results with spinosad, but please use reluctantly because resistance will build up in populations of CPB. The azadiractin has shown some efficacy, but neem works slowly. Generally it is used to reduce overall damage and reduce numbers but it is not a rescue treatment like spinosad is. NOTE: There is no longer a registered product for agricultural use in organic crops in the US that contains Bt tenebrionis as the active ingredient. Beauvaria bassiana (Mycotrol O) has been shown to suppress CPB populations though does not provide immediate control. And, using Beauvaria bassiana does not jive well with using crop rotation because you need the overwintered adult that remain infected with the fungus to eliminate buying the product new every year.

Asiatic Garden Beetle (Maladera castanea): I have received a few reports of activity of this critter. The Asiatic Garden Beetle is a native of Japan and China where it is not an important pest. The pest overwinters in the soil as a grub feeding on the roots in sod ground and weedy gardens. The larvae pupate early in the spring and the resulting adults emerge in June and start feeding on all sorts of garden vegetables. The adults are cinnamon-to reddish brown, rounded beetles. They eat big and irregular holes in the leaves and blossoms. You have to look hard to find them because they feed at night and burrow into the soil for the day. If you see chewed leaves and no pest, then go out at night with a flashlight and see who is there. It will probably be cutworms, or the Asiatic garden beetle.

If you have the problem, fall clean up with tilling the garden is important. Pesticides offer some control but often they are very numerous and seem to return from nowhere. Spinosad (Entrust and Montery Garden Spray) have been reported to work well.

Potato Leafhopper (Empoasca fabae): I have not had any verified reports of the potato leafhopper yet, and have not seen any. But, this is the time to keep an eye out for them. They could appear anytime, and remember, once you see severe damage from them it is too late to do anything. They primarily feed on beans, potatoes, eggplants, strawberries and alfalfa.. PLH does not over winter anywhere near here. They over winter way down south and leapfrog up here in mass migrations. The first to arrive are females, and they are usually carrying fertilized eggs when they get here. Then there are a few generations over the growing season before the cold north winter kills them.

Potato leafhopper damage, “hopperburn”. There is varietal difference in susceptibility but it is not clear enough to report. These are Satina on the left and Purple Majesty on the right. Photo by Eric Sideman.

The damage from leafhopper is catastrophic. The bug sucks the juice out of the plant and injects a toxin that clogs the food conducting tissue. The symptoms look like a disease after a while, rather than insect damage, and is frequently mistaken as such. The leaves first get pale, then yellow and then brown from the edges. Then the plant dies. The symptoms are called hopper burn.

The adult PLH is very light green and wedge shaped and tiny (an eighth of an inch long). The best way to find them is to brush the plant and watch one of the white-looking bugs land. The nymphs are similar to the adult, but have no wings and are even smaller and live on the underside of the leaves. If you disturb a nymph you will see it run and it can run sideways as fast as forward. This is a clue that you have PLH and not some other less harmful leafhopper.

The adults are flighty. When you brush your crop you will see them fly up. If there is a cloud of them, you are in trouble. Researchers have developed a threshold before treatment is recommended. Thresholds vary but here is one that is typical: Treat potatoes if 5 adults or 15 large larvae are found on 50 leaves.

Crop rotation does nothing for you since they are coming from far away. Covering your crops with a row cover would work, but these crops are not the type that are usually covered. Effective insecticides are limited. The only material that I have seen work that is allowed in organic production is pyrethrum, so Pyganic is the recommendation that I make. However, it does not work as well as a pyrethrum with PBO. BUT PBO is not permitted in organic production. If you market crops as organic, be sure to use an approved brand of pyrethrum, such as Pyganic. Use the most concentrated mix allowed. Spray late in the day or evening, get good coverage including the undersides of the leaves, and don't wait until it is too late.

Onion Thrips (Thrips tabaci): Onion thrips may become active soon, and if they have been a problem for you in years past it is time to start scouting for them. They are very tiny and easily overlooked until the onion plants start showing leaves that look as if they have been rasped. In fact they have. The thrips feed by using their moth parts to rasp and pierce the onion leaves, releasing juices for them to feed upon. If the population of thrips is large you will see silvery patches on all the young leaves and when really bad the whole field will look white and silvery and the leaves wither. Obviously onion yields can be greatly reduced because the onion plants loses food and water through the damaged tissue.

Onion thrips hide between the leaves at the base of the onion plant. I find the best way to find them is to pull up a plant and hold it upside down over a white sheet of paper and pull apart the leaves as you shake gently. Even when they are walking about on the paper you will still need to look hard to see the thrips. My eyes are not that good and I need a hand lens to even spot them. The immature thrips are white to a pale yellow, elongated with very short antennas and dark eyes. Remember, tiny. The adult is tiny too, but it has wings. Thrips' wings are unique. They are fringed with hairs. Thrips are very poor fliers, but they do fly when disturbed and get blown in the wind easily. Keep in mind that this means thrips will be blown to new fields downwind. Adults are pale yellow to dark brown.

There are many generations per season and they can be very quick in warm weather. Also, parthenogenesis is common, meaning females that cannot find males produce progeny all by themselves. Each female can produce up to 80 eggs, which tells you that the population can explode quite quickly under good conditions. Good conditions are warm and without heavy rains. Heavy rains wash the weak insect off the plant.

Growers can simulate heavy rains with heavy overhead irrigation. As well as disturbing the insect the extra water will help the rasped onions. Extra fertilization will help too.

Thrips survive in onion debris so clean up after harvest. I have heard that thrips are confused by inter-cropping with carrots.

If the natural enemies or the cultural practices fail to keep thrips populations down then you may need to turn to a pesticide. Remember, thrips are often around in small numbers which can be tolerated. IPM practices recommend an economic threshold of an average of 3 thrips per green leaf. When scouting, sample about 50 plants around the field from at least 10 different locations in the field and then figure the average per leaf. Entrust is the most common recommended material. Follow the label instructions and be sure to spray into the leaf axis.

Strawberry Clipper: The damage has been done by now and there is nothing to do about it. But large scale growers should be out assessing the damage and making the decision if it is time to rotate.

As with many of the problems of strawberry production, crop rotation to a distant field is the only way to manage the clipper.

For homeowners who just have a small patch of strawberries, now is the time to get out with a container and collect all of the clipped buds and destroy them.

The strawberry clipper is a small, copper to black snout nosed beetle. In the spring they emerge from overwintering as adults and begin feeding on pollen by poking holes into the bud (you will see holes in the petals when the flowers open).

Later the females lay eggs in the buds and then crawl down and girdle the bud so it hangs by a thread and dies. Each dangling bud has an egg in it. Each female can lay up to 300 eggs. These buds fall to the ground and development of next year’s clippers begins. You can see how a population of clippers can build very quickly over a few years in a strawberry field. That is why it is time for gardeners to collect those buds while they can see them, and why farmers depend on rotation.

Tarnished Plant Bug: Tarnished plant bug activity is very low to non existent so far this year, but now is the time to get ready. Last year their population was bigger than I had ever seen it and they essentially wiped out all early pepper and eggplants for me. The tarnished plant bug is a small (6 mm), bronze, brown and black bug that feeds on a very wide variety of plants. They overwinter as adults under debris and become active early in the spring. There are three or more generations per season. They are serious pests on strawberries (causing cat faced berries), lettuce (browning of midrib), flowers (destroying buds), eggplant and pepper (destroying buds), broccoli (brown beads in the head), and much more. They are common on potatoes where they basically kill flowers (who cares?). But last year the numbers were so high the damage tof the leaflets was extensive enough to be confused by many growers with late blight.

Now is the time to be managing them on peppers and eggplants; before they arrive. If you want early peppers and eggplants, cover them with row covers and keep them on until you see good flowers. It is pretty easy to kill the bug with pyrethrum, but not worth it because their numbers are so great in all the fields of hay and weeds surrounding you that any you kill will be replaced in a day or two. Weed management and timing of mowing neighboring fields is about all you can do to keep the numbers low. Do not mow fields when you have host crops in sensitive stages, e.g., strawberries with buds.

Three-lined potato beetles. Photo by Eric Sideman.

Cucumber Beetles On My Potatoes? No. Those are not cucumber beetles. Potatoes, tomatoes and sometimes eggplants are attacked by this pest that only superficially looks like a cucumber beetle. This is the THREE-LINED POTATO BEETLE. The adult of this pest is about the same size as a cucumber beetle but has a reddish head and a thorax with two dark spots. The wing covers are dark yellow with three black stripes. Its favorite food in my experience is tomatillo.

The Three-Lined Potato Beetle overwinters as an adult and wakes early in the spring. They are there waiting for you to plant your solanaceous crops. The females soon begin laying eggs that hatch in about two weeks to larvae that look a bit like Colorado potato beetle larvae, except these critters have the endearing practice of carrying a small pile of their own excrement on their back. The larvae mature in about two weeks. There are probably two generations per year.

On most crops the level of the pest does not warrant control. If this pest has been a problem in the past, floating row covers will help you avoid the overwintering adults and that should get you by. Hand picking will work on small plantings. Pyganic and Entrust may offer some relief. Rotenone works well, BUT REMEMBER THAT THERE ARE NO ROTENONE FORMULATIONS THAT MEET ORGANIC STANDARDS.

Pythium diseased pea plant.
Photo by Eric Sideman.

Pythium Diseases Of Peas: There are several species of Pythium that cause pre and post emergent diseases that effect the seed (seed rots), seedling (damping off), and roots (root rots) of peas and beans. We are all familiar with damping off of seedlings caused by Pythium, but it can cause problems in older plants too. Once the plant emerges and develops mature cells with thicker cell walls, Pythium is less likely to be a problem, but it still may attack the young cells at the root tips and lead to “root pruning” and stunted, chlorotic plants. Pythium diseases of seeds and seedlings results in gaps in plantings where seeds have simply rotted away, or stunted seedlings simply died shortly after emerging. If your plants begin to yellow and are stunted, and the roots seem feeble, Pythium is a likely culprit. With this very wet early start to the year I am seeing some of this.

Close-up of roots of Pythium diseased pea. Note lack of young roots. Photo by Eric Sideman.

Pythium spp. are common soil inhabitants with a wide host range, which makes crop rotation less effective. The pathogen can survive for many years with no host at all in root debris as resistant spores or sporangia. High soil moisture is necessary for the disease to become a problem for peas or beans.

Anything you can do to get the soil to dry will help. In the future, avoid using old seed with low vigor. Deep plowing to bury root debris has been shown to reduce the disease in some studies. Avoid wet soils when you can.
Biological control agents may be useful as seed treatments. Actinovate AG (Streptomyces lydicus), MycoStop (Streptomyces griseoviridis), and T-22 HC (Trichoderma harzianum) are labeled for Pythium, but I have not yet heard about the efficacy of these.MOFGA's Pest Report - June 1, 2011
Compiled by Eric Sideman, PhD - MOFGA's Organic Crop Specialist

Wet: Although it seems as if we are out of the woods because it has not rained in a while and soils are mostly dry enough to work, there is still plenty of time to worry. Last week I discussed the loss of nutrients to leaching and other paths. Now, looking at my yellow, stunted severely and some dead spinach I thought I should mention that roots need air as much as leaves do. Because the spaces between the soil particles were filled with water for too long, the roots stopped functioning, and some may have died. You may look at your pale plants and make a decision to hope for the best, or replant.

Grey mold: (Botrytis cinerea) is a fungus that you cannot run and hide from. The spores are blowing everywhere. It is a very common problem on soft fruits (e.g. strawberries), all sorts of flowers, and sometimes leaves and stems. We organic growers must be aware of the conditions that favor the fungus over our crops and do our best to manage them. Botrytis is favored by cool, rainy, foggy and generally moist situations. The reason there is still time to worry even though the weather has improved is that the initial infection is usually on senescent tissue, for example the old petals and sepals of strawberry flowers, wounded stems or leaves, etc. And then it can spread from there if the conditions are right, or get right again to favor the fungus over the crop.

Even though you may not spot the problem until you are harvesting strawberries when you see the typical gray fuzzy mass of fungi and spores, the initial infection took place during bloom. And, during bloom this year it was wet. Also, Botrytis can be a problem in weedy fields or where the foliage is too dense, e.g., the lower leaves of a lush row of tomatoes (especially in a high tunnel) or lower leaves in the dense growth of potatoes. Essentially, where the plant tissue stays damp and cool for a while there is a risk of Botrytis, especially if there is senescent tissue. Last year I was getting many people calling with fear they had late blight when really they had Botrytis gray mold. If you get the typical gray fuzzy growth it is easy to tell. On leaves before spores are produced it is a bit harder. Gray mold will form lesions on leaflets of potatoes or tomatoes and progressively expand to include the whole leaf and then the petiole and stem. Lesions on lower parts of the stem may girdle it and the plant will wilt. A key distinction from late blight is the lesion usually is associated with yellowing of the leaf.

After the rainy weather most of us experienced this spring, I suggest you pay close attention to anything that would lead to damp conditions. What I think is really important now is to get the weeds under control, do not allow foliage to get too dense, and use wide spacing between rows of crops.

Potato Seed Problems: Once again I am getting reports about Fusarium dry rot on potatoes bought for seed. This is a very common potato storage problem, and also on potato seed. Conventional growers commonly treat potatoes going into storage, or to be used for seed, with fungicides to control the problem. The problem begins at wounded spots on the potato. Brown lesions form and the infection slowly develops into cracks and cavities in the potato. White cottony growth may occur. And, if the problem persists then secondary bacterial infections occur and the potato becomes soft and watery.

Fusarium spores are really common and are a cause of seed piece decay. The most common cause of the disease in the new crop is though planting diseased seed pieces. Do not plant any potato seed that is obviously displaying Fusarium dry rot. When cutting seed pieces, do not cut diseased seed pieces and then go to use the same knife for healthy seed. Planting whole seed pieces is safer.

The one piece of good new is that it is not late blight, which is the worry of the people calling me.

Potato seed pieces with Fusarium dry rot. Photo by Eric Sideman.

Late Blight in tubers. Photo by Steve Johnson.

Striped Cucumber Beetle: (Modified from article in Mass. Veg. Notes written by Ruth Hazzard & Andrew Cavanagh, University of Massachusetts, updated for 2010.)

Striped Cucumber Beetles. Photo by Eric Sideman.

Striped cucumber beetle is our most serious early-season pest in vine crops. I have already had reports of the first ones showing up in southern Maine. These beetles spend the winter in plant debris in field edges, and with the onset of warm days and emergence of cucurbit crops, move rapidly into the field. Densities often are very high, especially in non-rotated fields or close to last year’s cucurbit crops. Management cannot wait because adult beetle feeding on seedlings (cotyledons and young leaves) is the most serious, and can cause stand reduction and delayed plant growth. Also, the striped cucumber beetle vectors Erwinia tracheiphila, the causal agent of bacterial wilt, and this may be more damaging than direct feeding injury. Crop rotation, transplants, and floating row cover are cultural controls that help reduce the impact of cucumber beetles. By far, floating row covers offer the best results. You must get the row cover on at transplanting or seeding. Early management is important to avoid early season infection with wilt. Cucurbit plants at the cotyledon and first 1-4 leaf stage are more susceptible to infection with bacterial wilt than older plants.

Perimeter trap cropping gives excellent control with dramatic reduction in pesticide use (see following short article).

Beetle numbers should be kept low, especially before the 5-leaf stage. Scout frequently (at least twice per week for two weeks after crop emergence) and treat after beetles colonize the field. Early spot treatments of field edges can be helpful. The threshold depends on the crop. To prevent bacterial wilt in highly susceptible crops, we recommend that beetles should not be allowed to exceed one beetle for every 2 plants. Less wilt-susceptible crops (butternut, most pumpkins) will tolerate 1 or two beetles per plant without yield losses. Spray within 24 hours after the threshold is reached. Proper timing is key. Pyrethrin should be spray very early in the morning, at dawn or before, to catch the beetles before they become active with the day’s warmth, and to give the pyrethrin time to work before the sun degrades it. Evening spraying can work for that, but often the beetles are flighty then and you see them flying up and away as you move down the row.

OMRI-listed insecticides available for use in striped cucumber management include kaolin clay (Surround WP), pyrethrin (Pyganic Crop Spray 5.0 EC), and spinosad (Entrust). In 2009 spray trials comparing these three products at the UMass Research Farm, kaolin was the most effective in reducing beetle numbers and feeding damage. There was a trend toward Surround WP being more effective when Pyganic or Entrust was mixed with it, but never significantly better than Surround alone. Other studies have shown more efficacy from pyrethrin and spinosad. Remember, Surround should be applied before beetles arrive because it acts as a repellent and protectant -- beetles do not “recognize” the plant and so do not feed -- not a contact poison. With direct-seeded crops, apply as soon as seedlings emerge if beetles are active. Transplants can be sprayed or dipped into the solution before setting out in the field.

I just heard from a grower who tried out a vacuum yesterday and reported that it seemed to work well. He suggests using a vac with a low setting and/or a broad nozzle so that you don't damage plants. Also, do this earlier in the morning when they are sleepy and slow and be sure to look in their hiding places under the plants.

Perimeter Trap Cropping For Cucumber Beetle Management: (Reprinted from Umass Veg. Notes)
Over the past years, you have probably heard a lot from us [Ruth and Andy at UMass] about perimeter trap cropping to manage striped cucumber beetle in cucurbit crops. The system has proven itself as an effective, cost-saving method for managing this pest. Systemic or foliar insecticides in the trap crop border are effective in halting the beetles in the border and protecting the main crop. PTC systems can reduce insecticide use by over 90% if implemented correctly, but this is not the only benefit. By spraying only the border of your crop you’re leaving the main part of the field as a refuge for pollinators and natural enemies of insect pests. Leaving the main crop unsprayed may also help to delay the development of insecticide resistance in the striped cucumber beetles – a few beetles will always bypass the border, and thereby escape selection for resistance. The first trap crop that we looked at was Blue Hubbard, but many growers told us that Blue Hubbard is difficult to market and other border trap crops were needed. We evaluated buttercup and kabocha squash as alternative border crops, and they worked just as well as Blue Hubbard. Markets for these crops are strong. Any Cucurbita maxima variety is likely to be very attractive. This species includes many giant and specialty pumpkin varieties; the only one we do not recommend as a border crop is Turk’s Turban because unlike most C. maxima varieties it is highly susceptible to bacterial wilt which is vectored by the beetles. You can even plant a border of mixed C. maxima around your butternut squash, acorn squash, and other winter squashes that are C. pepo, or C. moschata types. This will provide you a wide variety of interesting squash to market. We’ve tested this system extensively and found that as long as the trap crop border is planted on good land and remains intact the system works remarkably well. In most cases, growers who use this system never need to apply insecticides to their main butternut crop at all. In Connecticut, they’ve found the system to work equally well with cucumbers and summer squash. Zucchini tends to be more attractive than summer squash, and some varieties such are so attractive that they could be used as a trap crop. We’ve also seen PTC work well in pumpkin crops, as long as the pumpkins in the main crop are C. pepo and not C. maxima. Remember, many giant and specialty pumpkins are actually C. maxima species, and would make good trap crops. On organic farms, growers often treat the main crop with kaolin clay (Surround WP) which serves as a repellent. For transplants, using this before planting is very efficient and lasts for a week or so if there are not heavy rains. Spinosad or pyrethrin could be used in the border. Every year we talk to more growers who adopt this system. The reduction in pesticide costs can be dramatic, and more than offset the small amount of time and care it takes to plant and treat a solid perimeter trap crop. If you would like to try this system and have any questions, or just want to find out more about how it works, please call Andy Cavanagh at 413-577-3976.MOFGA's Pest Report - May 20, 2011
Compiled by Eric Sideman, PhD - MOFGA's Organic Crop Specialist

WET: Here in the Northeast, actually throughout most of the country, it is wet. Wet and cold. Even though Becky repeatedly tells me not to worry about things over which I have no control, I worry. In addition to worrying about the fruit trees blossoming with no bees out of their nests, about weeds taking over fields way to wet to pass over with a tractor, about seedlings getting way to large for their container, and on and on, I also am worried about fertility, especially nitrogen. The fertility I laid when I put out the few things I was able to before the rains began may be gone. For example, any of the nitrogen that was in a soluble form before the four inches of rain we got this week fell is washed away. And much of the nitrogen in the soil in nitrate form before the soil became water logged and anaerobic has been lost to the atmosphere through denitrification. See the last issue of the MOF&G for a detailed discussion about nitrogen fertility. The take home message; once we dry out, think about crop fertility.

Flea beetle feeding is very intense some years. Photo by Eric Sideman.

FLEA BEETLES IN BRASSICAS: Flea beetles have begun feeding in spring plantings of brassica crops. Numbers are likely to rise in coming weeks as beetles move out of field borders where they spent the winter. Crucifer and striped flea beetles feed on Brassica crops as well as weeds that are in the same family, such as yellow rocket or wild mustard. [It is a different species of flea beetles that feeds on the tomato family of crops. This is important information when planning rotations of potatoes or tomatoes with Brassica crops or Brassica cover crops].
The crucifer flea beetle (Phyllotreta cruciferae) is uniformly black and shiny, about 2 mm in length, while the striped flea beetle (Phyllotreta striolata) has two yellow stripes on its back. Flea beetle adults feed on leaves and stems, resulting in numerous small holes, or ‘shot-holes’. Eggs are laid in the soil starting in late May, and beetle larvae feed on roots. The non-waxy greens (arugula, bok choi, tatsoi, mustard, Chinese cabbage, komatsuna) are preferred to the waxy cabbage, kale and collard types of brassicas. In Brassica greens, beetles feed on the whole surface of the leaf, and will continue feeding from the seedling stage until harvest. Waxy crops are most susceptible at the cotyledon and seedling stage, then feeding is more limited to leaf margins on older plants. Some crops simply out grow the beetle pressure and the damage can be tolerated. No damage can be tolerated in crops such as arugula.

To reduce and delay flea beetle invasion of spring crops, plant them as far away from the fields that were used for fall Brassica crops as possible. Beetles overwinter in field borders near last year’s crop. Planting the same crop close by to where it was last year ensures a high population in the spring. The same could be true if you have fields full of mustard weeds.

Flea beetle trying to get in but Proteknet is keeping it out. Photo by Eric Sideman.

One of the best ways to protect Brassica crops from flea beetles is to place a floating row cover over the bed or row. It is critical to seal the edges immediately after seeding or transplanting, because Brassica seeds germinate quickly and beetles rapidly find the cotyledons. Flea beetles can fit through extremely tiny cracks. Edges of the cover must be sealed on all sides using soil, plastic bags filled with soil, or some other method. [NOTE: There is a new product out there called Proteknet. It is distributed by Dubois Agrinovation out of Canada, and Fedco is selling it this year too. It is, as the name implies, a fine net rather than a spunbound covering. It is said to have a 5 year or more life. See the web version of this Pest Report for a picture.]

If cultural methods fail, you may have to turn to a pesticide. Spinosad (Entrust is the organic formulation) is proving to be effective in suppressing flea beetles and reducing damage. Pyrethrin (Pyganic EC 5) showed poor to moderate efficacy in trials, and has a short residual period. Yet some growers have reported a good knockdown with this product. You can spray the Pyganic right through the row covers and knock down any flea beetles that may have gotten inside.

DOWNY MILDEW IN LETTUCE: Downy mildew is caused by a fungal-like water mold. It can be a problem where temperatures are low and leaves are wet for long periods, as it is this week. Downy mildew is more often seen in fall and early winter production in hoophouses. Downy mildew first appears as light green lesions (photo 3.6 at right). Later, the leaf develops a yellow, chlorotic appearance. Older lesions turn tan and then papery (photo 3.5 at right). When the weather is just right to favor the fungus it produces sporangiophores and sporangia that poke out of the stomata on the underside of the leaves. These appear as discrete white projections. Downy survives between crops as mycelia and oospores in crop residue in the soil.

Crop rotation is the first line of defense. Plow deeply after harvest to bury the diseased crop residue. Minimize leaf wetness (drip irrigation instead of overhead, orient rows parallel with prevailing wind, use wide spacing, control weeds, etc.). Avoid planting lettuce in poorly drained fields. There are no known organic materials that are effective.

FUSARIUM WILT OF PEAS: Peas are susceptible to wilt diseases caused by a soil-inhabiting fungus called Fusarium oxysporum. There are a handful of different races of this species and this is an important point because the best defense against this disease is using resistant varieties, and resistance is race specific. In other words, just because the seed catalog say that the variety is Fusarium it may not be resistant to the particular race that is in your soil.

Fusarium wilt of peas in advanced stage. Note plants die from base up to tip. Photo by Eric Sideman.

Symptoms of Fusarium wilt includes early downward turning of the leaves and then yellowing of the plant from the base up. When temperatures are warm the disease progresses rapidly and the entire aerial portion of the plant dies. Unlike Fusarium root rot of peas, which are caused by a different species of Fusarium, the roots of peas dying from Fusarium wilts appear normal. Still, if you slice open these “normal” roots you will see that the vascular tissue in the root is affected and discolored to an orange or yellow.

Fusarium wilts can be carried on the seed, and spread by movement of infected soil or crop debris by wind, water or people. Once you get the organism in your soil you are stuck with it. Fusarium can persist in the soil as very resistant spores called chlamydospores for a decade or more, even without a host pea plant. Crop rotation is still important to avoid building large populations of the pathogen in the soil. Avoid moving soil or crop debris from fields known to be infected, i.e., clean equipment and boots between fields.

The best control of Fusarium is to use resistant varieties. If you get it, avoid letting the soil dry because this will make disease progress more quickly.

LATE BLIGHT: Late blight has been found in Maine in a greenhouse where tomatoes were alive through the winter. At this time the plants have been destroyed. Late blight only overwinters in our region in living tissue; that is in the potato tuber and host crops kept alive in greenhouses. These overwintering hosts are the potential source of any outbreaks of late blight. If you have kept late blight hosts alive through the winter be sure to carefully monitor them for any symptoms of the disease. If you suspect that tomato plants in your greenhouse may be infected, immediately contact someone who can positively identify the problem. DO NOT TRANSPLANT, OR SELL FOR TRANSPLANT ANY TOMATO PLANTS FROM A GREENHOUSE WITH INFECTED PLANTS.

As the season progresses make sure you scout your fields for any sprouting volunteer potato plants and destroy them. Plant only clean potato seed.

We are always at risk from poor practices of others, and the blowing wind, but for sure let’s all do our part to avoid filling the air with late blight spores.

WIREWORMS: (Modified a bit from an article in Becky Sideman's UNH Vegetable Newsletter). This is the time to decide where you are putting the different crops. Now is your chance to avoid wireworm problems because once you see the damage it is too late. Wireworms damage root and tuber crops such as potatoes, sweet potatoes and carrots by tunneling, causing unsightly holes as well as providing an entry point for pathogens. Young seedlings with small root systems can be weakened or killed. Favorite young seedlings of wireworms include peas and artichoke.
This is the time to decide not to put these host crops where there are large populations of wireworm, which includes land recently in sod, or near the edges of fields where wireworms can migrate from the sod headlands.

Life of the Wireworm. Wireworms are the larvae of click beetles (family Elateridae). There are many species of wireworm. The larvae have slender, hard, ≤ -1 inch long bodies that range from tan to orange to brown in color. The larvae pupate in the spring, and the adult beetles emerge and are active in the summer. The adult beetles are not typically pests. Female click beetles lay eggs during May and June. They lay eggs in the soil, primarily in weedy or grassy fields. The eggs hatch in 3-4 weeks, and the larvae then look for food. The larvae can live for several years, depending on the species, availability of food, temperature, and soil moisture. Because eggs are typically laid in grassy fields, wireworm problems are usually most severe in fields that were recently sod. However, because the larvae can live for many years, problems can persist in fields that have not been sod for some time. And grassy cover crops can attract the adults for egg laying. Wireworms are often more prevalent in moist areas of fields, and in areas with high organic matter.

What they Eat. Wireworms are omnivores. They feed on the roots of grasses or weeds and on other soil insects. It is hard to starve wireworms out of a particular area, because of their diverse diet. Crops that tend to increase wireworm populations include potato, carrot, sweetpotato, small grains (wheat, barley), onion, beet, and clovers. A clean (non-weedy) alfalfa crop can reduce populations. This may be in part because of alfalfa's deep root system reduces soil moisture, making the environment less favorable for the larvae.

Minimizing Damage. Rotation into alfalfa or crops that are not preferred can reduce wireworm populations. Avoid planting highly susceptible crops such as potato and carrots into sites with a high potential for damage, such as fields previously planted to grass sod, pasture or small grains, or fields with a prior history of wireworms. The edges of fields (near sod) can also be a problem, because the larvae can move through the soil in search of food. Baits can be used to determine wireworm pressure prior to planting a susceptible crop. This can be done by placing carrots or potatoes in a softball-sized hole about 4-6‰ deep, covering with loose soil, and then covering the area with a piece of black plastic to warm the soil. Wait 4-7 days, and dig up the bait to check for the presence of wireworms before planting. On small scale plantings this baiting system can be used to reduce numbers in gardens. Another version of this method involves burying a fist-sized clump of corn, wheat, or rolled oats. It may also help to harvest crops as soon as possible. Some reports indicate that the wireworms seek out the moisture in potato tubers if soil conditions become dry, and wireworm damage increases over time in potato crops left in the ground.

CUTWORMS: (many species). Cutworms are occasional pests of many crops early in the season, including carrots, peas, onions, spinach, broccoli and the list goes on and on. Some years they result in major losses, other years result in no loss at all. They are larvae of a dozen or so different species of night flying moths. They are greasy looking caterpillars that have a habit of curling into a “C” shape when disturbed. Most species that attack vegetables overwinter as partially grown larvae and so can become active very early in the spring when the plants first germinate and are very susceptible. Cutworms hide in the soil during the day and crawl on the surface at night. They feed and cut off young seedlings at the soil surface.

Cultural Control. Since most species lay their eggs in the late summer/fall on vegetation, keeping fields clean of weeds and crops in the fall helps. Of course, this goes counter to the recommendations to keep the soil covered cropped, so it is a management decision based on how bad the problem has been. Fall plowing exposes larvae to birds. Cultivating fields in the spring just after vegetation has appeared and grown a few inches, and keeping it clean cultivated can starve the cutworms out before the peas go in. But, in must areas this is not practical because crops need to be planted.

Materials Approved for Organic Production. Entomopathogenic nematodes show good efficacy when environmental conditions are favorable. Steinernema carpocapsae has been shown to be very effective against cutworms, although reports are not specifically in pea production. Success with nematodes depends on proper application methods. Be sure to follow the instructions from the supplier carefully. A few suppliers of these insect-attacking nematodes are The Green Spot (www.greenmethods.com), IPM Laboratories (www.ipmlabs.com), and ARBICO (www.arbico.com).

Baits. Spinosad or Bt will kill the caterpillars, but getting the pest to consume the insecticide as a sprayed on material before significant damage is done is not likely. However, farmers have reported good results using these materials in baits. The bait is spread on the ground near the plants, or prior to planting to clean out an area.

Spinosad - Seduce (OMRI Listed) is a new commercial bait. I have no experience yet with this, so if any of you try it, please let me know what you think.

Bt - A bait made from Bt is often recommended and has received good reports from farmers. This is a method of use of Bt that is not described on the label. This off-label use is permitted by EPA under FIFRA 2ee, but growers should check with their state pesticide regulators about their state regulations. Make the bait by mixing the highest concentration solution of Bt allowed on the label and then mixing in a bit of molasses and alfalfa meal or bran. Then dampen this mix if necessary. Spread the bait along the planted or planned rows in the evening.MOFGA's Pest Report - April 11, 2011
Compiled by Eric Sideman, PhD - MOFGA's Organic Crop Specialist

The first Pest Report of 2011 and the forecast today is for 70 degrees. The topic for this issue has to be "don’t be fooled and don’t rush." There are many insect and diseases of plants that take advantage of a crop that is struggling. Looking out my window I see signs of spring that could easily get growers out on their tractors or behind their tillers. My warning is to not grow by the calendar or a stray warm day. Today is warm, the calendar says mid-April. But, here at my farm we still have cold and very wet soil. In order to avoid setting your self up for problems, wait for the conditions to be favoring the plant and not the pest. Here are a few of the problems lurking in the shadows of a faux spring.

SEEDCORN MAGGOT (Delia platura)
The seedcorn maggot is a larva of a fly. The maggot mostly feeds on decaying vegetable matter in the soil, but if seeds are slow to germinate they fall prey too. Peas and beans are the most commonly injured seeds because people rush peas into the ground early in the spring and beans are slow to germinate in cool soil no matter what the calendar says. Corn, melons, cucumbers, potato sprouts, cabbage, beet, onion (here often confused with onion maggot), spinach, radish and more crops are also frequent victims.

The fly lays its eggs in moist soil. They are attracted to soil high in fresh organic matter. The fly eggs can hatch at very low temperatures. The larva feed on the seed, especially the embryo. Seeds may be killed before they sprout, or may sprout but be missing parts such as a cotyledon or growing tip. I often see beans germinate that have two cotyledons but no more growth because this pest ate the growing tip.

Cultural Control
Everything that can be done to encourage and hasten seed germination is important in early spring plantings. For example, waiting for warm soil, waiting for a good 5-day weather forecast, planting shallowly, etc. Slow to germinate seeds are sitting ducks for the seedcorn maggot. Avoid adding organic matter that is not fully decomposed to fields of early spring planted crops (ex. unfinished compost, livestock manure). Clean cultivation is recommended for early plantings.

DAMPING-OFF IN THE FIELD
Below I will discuss damping-off of seedlings in greenhouses and on window sills. Last year I received calls about peas dying just after or just before germinating and I thought I better mention that damping off can also occur in the field. This time of year the problem is with peas.

The disease is caused by several different species of Pythium, which is a common soil inhabitant that persists in soil (often in root debris) as spores. The species have a wide host range of crops and weeds and so crop rotation will do little to avoid the problem.

During or just after germination the pea seedling begins to show symptoms. The symptoms may be as simple as yellowing and stunting because sometimes only the root tips are infected and this root pruning interrupts growth. Sometimes a soft rot of the stem kills the plant. Sometimes you just don't see any peas.

High soil moisture and warm soil temperatures (warmer than optimum for pea growth, i.e., 65-75) favors Pythium. You can't control the weather but you can choose when you plant your peas. If the soil is very wet and warm weather is forecast it may make sense to delay planting a few days for the soil to dry a bit.

There are resistant varieties. The resistant gene is tied to some visual characteristics of the seed. Wrinkled seeds are more severely affected than round seeds. Also, some biological seed treatments such as Rootshield may help.

CABBAGE AND ONION MAGGOT (Reprinted and modified from The Umass Veg Notes)Onion maggot (Delia antiqua) and cabbage maggot (Delia radicum) flies look nearly identical but are likely to be found only on or near their host crop. Cabbage root maggot attacks all types of Brassica crops, while onion maggots are highly specific for the onion family including onions, garlic, leeks, chives, and shallots. A good indicator of the start of cabbage root maggot flight is blooming of the common roadside weed, yellow rocket.

Life cycle: Onion and cabbage maggot flies spend the winter as small brown pupae in the soil. Adults emerge in spring and adults can travel considerable distances in search of host plants (1/2 to 1 mile). Cabbage root maggot flies are rather delicate, hump-backed gray-brown flies, about 5-7 mm long. Onion maggot flies are very similar. Female flies seek out their host crop to lay eggs at the base of the stem. Cool, moist soil conditions favor survival of the eggs, and soil temperatures over 95 F kill them. When the soil temperatures in the upper half to 1 inch are high (>95 degrees F) that soil temperature itself then provides control. Last year we reached these conditions in April, but it didn’t help because eggs were not yet present. This is the reason these pests were still a problem last year, and are a usual problem in the spring. Summer generations of the pest are rarely noticed.

When eggs hatch, larvae feed on roots and can cause complete destruction of the root system. In crops such as broccoli or cauliflower the first sign of a problem is wilting of the plant on sunny days and yellowing of outer leaves. Later, plants collapse, wilt down, and die. If you pull one up you will see that the reason it is wilting is the roots are gone. You may find the legless white maggots feeding, or the small brown, oblong pupae. In Brassica root crops such as turnips, radishes and daikon, feeding tunnels make the root unmarketable.

In onions, newly hatched larvae crawl behind the leaf sheath and enter the tiny bulb, and feed on the roots, stem, and developing bulb. Feeding damage also encourages entry of soft rot pathogens.

Avoiding damage by later planting. The first flight and egg-laying period is generally most intense in the first half of May, depending on accumulated growing degree days – thus, it will vary with the season and location. After the first flight is over, and as soils heat up, fewer eggs are laid and those that are laid are less likely to survive. I have observed that in most years that Brassica transplants set out after the flowers fall from forsythia did not suffer damaging infestations of cabbage maggots. In cooler areas of the state, however, scouting has sometimes found damaging levels into June. Each season will be different. It is impossible to name a consistent and reliable date after which it is safe to plant onions or cole crops, but late May into June will likely be safer than the first half of May. By the way, if you find that your early May plantings of onions were hit hard, there would still be time to do another planting that would be less at risk. And, there would be time for many more plantings of brassica crops.

Monitoring. Flies are attracted to bright yellow colors. Yellow sticky cards (3X5 inches) are inexpensive and easy to use; attach them with small wire stakes and place near the soil. Check and change traps twice weekly to record changes in fly activity. (sources: Great Lakes IPM, Gemplers)

Using Growing Degree Days. The beginning and peak of each fly generation can be forecasted using degree day accumulations. Most growing degree day information for
plants and insects is based on a base temperature of 50 F, but maggot flies are active at a lower base temperature of 40 F. For more information on using growing degree days, go to http://www.umassvegetable.org/ and look at the May 6, 2010 issue of the Umass Newsletter.

Control
Floating row covers provide an effective barrier against these pests. Place the cover on as soon as the transplants are set. Use in a rotated field, as flies overwinter in soil after late season crucifers and could emerge under the cover if the same field has spring brassicas. Replace cover after weeding operations. As soil temperatures rise, the first flight ends and crops grow large, covers can be safely removed.

Crop rotation contributes to keeping populations low; greater distances are more effective. Fall tillage to bury crop residues and to expose over-wintering pupae is also useful. For onions, bury or haul away onion cull piles. Rotting onion smell attracts the onion maggot fly. In an vigorous Brassica crop, cultivation that brings soil up around the stem may help encourage formation of adventitious roots from the stem, which can help compensate for root loss even if maggots are present.

Naturally-occurring fungal diseases occasionally will reduce onion maggot numbers significantly, particularly when flies are abundant and relative humidity is high. During a fungal epidemic dead, diseased flies, can be seen clinging to the highest parts of plants along field edges. Predaceous ground beetles, which eat onion maggot eggs, larvae and pupae, can also be important in reducing maggot numbers.

Nematodes for biological control. One alternative method that has shown promise but has not been widely field-tested is soil application of entomopathogenic nematodes, especially Steinernema spp. Steinernema feltiae has been found to be more effective compared to other Steinernema or Heterorhabditis species in attaching to and penetrating cabbage root maggot larvae at low temperatures (10C) which is an important trait for use in spring when soils are cold. Common application methods include suspension of nematodes (infective juveniles) in water and application of water to transplants prior to setting in the field (as a spray or soaking drench), in transplant water used in the water wheel transplanter, as a drench after transplanting, or a combination of pre-plant and post-plant applications. Rates of 100,000 to 125,000 infective juveniles per transplant have been shown to be needed to achieve reduction in damage.

SEEDLING PROBLEMS
Raising seedlings in a "sterile" mix such as Pro Mix is easy. These mixes are called sterile, however they are not really sterile. On the other hand they are called sterile by growers because they don't have plant pathogens in them, and that beats my home-made mix. These "sterile" mixes are mixes of pathogen free materials such as peat, perlite, vermiculite with synthetic and very available sources of plant nutrients added in just the right amount to get newly germinated plants off and growing. Organic growers do not have the option to use these mixes. We either purchase mixes that are generally based on compost, or mix up our own. Seedling problems are much more likely in organic mixes because of the possibility that the compost may be carrying plant pathogens. In addition, it is much more difficult to predict the availability of nutrients from natural sources because of how biological activity is greatly affected by temperature, moisture and other factors. Many commercially available organic mixes are quite good and consistently free of pathogens, and good with nutrients, but occasionally even these fail. Home made mixes, such as the one I make, fail more regularly. Here are some of the problems I have seen frequently in my home made mix, and occasionally in commercial mixes.

Damping-off
Damping-off is a disease most commonly seen in young seedling but may rarely effect older seedlings. It is caused by species of fungi that commonly live in the upper layers of soil and when things are not right these pathogens jump at the opportunity to infect germinating seeds and seedlings. The two most common species that cause damping off are in the genera Pythium and Rhizoctonia.

There are two types of damping off. The first is one growers often misinterpret because it is pre-emergence damping-off, which rots the sprouting seed before it breaks through the soil. Growers often blame the seed companies for poor seed. The fungus attacks any part of the germinating seed especially the tiny growing tip. Post-emergence damping-off begins as a lesion on the root which extends up the stem to and/or above the soil line. The young stem is constricted by the attack and becomes soft, and the plant falls over and dies.

Damping off cannot be cured but it can be prevented by starting seeds in better conditions (or the "sterile" media). First make sure you are using seeds of the highest quality. Old, mistreated, and weak seeds are more susceptible to damping-off. Anything that slows germination increases the risk of infection. Excessive watering, poor drainage and less then optimum temperatures should be avoided. Allow the surface of the container to dry a bit before watering.

It is possible to "sterilize" your media by baking the mix in the oven at 3500 F for about 45 minutes. The mix should reach 1600 and should stay at that temperature for 30 minutes. Do not allow it to go higher or stay hot longer because overheating kills the beneficial microorganisms and may releases toxic materials

Cold Soil/wet soil
In addition to damping off, cold soil can cause other problems. Growing seedlings on window sills is often a problem because of cold night time temperatures. The roots of plants do not function when cold and plants frequently display symptoms of malnutrition even thought the media may have plenty in it. Purple undersides of leaves, stunted growth, pale weak seedlings are often the results of “cold feet” or “wet feet”. Trying to grow a tiny seedling in a large container may have the same effect because the plant is just not big enough to use the water and over watering may be a problem the plant cannot get out of.

Salt
Some composts are high in soluble salts. Even if the salts are nutrient salts such as nitrates, high salts will cause water absorption problems and may prevent seeds from germinating. Salty composts are not a problem in field use because they become diluted with the soil, but in a seedling media it is a real problem. Compost used for media should be the best you can get and should not have salts -measured as conductivity on a compost analysis- higher than 1mmhos.

Carbon:Nitrogen
The C:N ratio is critical for compost used in potting mixes. A high C:N ratio will result in nitrogen lock up, which is a case where all the nitrogen in the media, and any you add with fertilizers, is being grabbed by the bacteria feeding on the carbonaceous material. It is a sign that the compost was made from an improper mix of feedstock, or perhaps is just not finished yet. Compost used to make media should have a C:N ratio of 15:1 to 18:1.

Ammonia
As nitrogen is released from decomposing proteins in a compost pile it passes through a phase where it is an ammonium ion. Unfinished compost will have ammonium ions that may revert to ammonia and kill roots. Ammonia nitrogen in a compost used for a potting soil should be less than 0.1%. Problems from high ammonia can be seen as very weak, dying seedlings, and when you pull them up you see that the roots are brown instead of a nice healthy white.

My recommendation is to get an analysis of any compost you plan to use to build your own seedling mix. The University of Maine Soil Testing Laboratory does compost testing. Just be sure that if you send a sample to follow the directions and ask for the compost analysis. If you are buying a commercial compost based mix you may want to speak to other growers and see how that brand has worked for them.